Can we use a messenger that does not alter the AI to solve the control problem?
I would say no due to the possibility of psychological manipulation of the messenger by the AI. Also, the LED communication constraints place severe limitations on the capabilities of the AI, as the usefulness of AI is likely predicated on its ability to learn quickly from a vast amount of information (e.g. using the internet). 

In some sense you may successfully control an AI using techniques like this but the nuance of the control problem is controlling an AI without restricting its ability to solve our greatest problems. 

We already knew that we could keep an AI safe inside a computer isolated from the rest of the word, but the problem fundamentally is that we if had a truly general AI, we would never want to keep it isolated. Is there some way to unleash it so that it is fully capable of solving our problems while simultaneously making sure that it is safe?